The proposed research is designed to examine processes of contrast (pattern-selective) adaptation in the human visual system, and how this adaptation regulates the perception of color and form in stimuli characteristic of the natural visual environment. Sensitivity to color and form can be strongly influenced by adaptation to the chromatic and spatial properties of natural scenes, yet the implications of these sensitivity changes for visual coding remain poorly understood. The goal of the present proposal is to examine the functional consequences of adaptation, by exploring how adaptation alters the relative salience of color or form within scenes. Measurements and analyses of natural scene statistics will be combined with psychophysical studies that probe both perceptual and performance measures of visual salience and how it varies with natural variations in the observer's state of adaptation. The specific aims of the project include measurements to characterize I) how the perceptual salience of color depends on the color properties characteristic of natural backgrounds, and how color salience is affected by adaptation to the background; 2) how adaptation to the characteristic spatial structure of images influences the salience of structure at different spatial scales in images; and 3) how adaptation to natural spatial configurations alters the relative salience of different image configurations. The latter experiments focus on human face perception and how the salience of natural facial configurations may be biased by the large changes that adaptation induces in the appearance of faces. The results of these studies would be important for understanding how pattern-selective adaptation modulates perception and performance, and thus for understanding the possible roles that the adaptation plays in visual coding. Assessing these effects in natural viewing conditions is important for revealing how adaptation influences the natural operating characteristics of the human visual system, and thus for understanding the implications and consequences of visual dysfunction.